1. The Field of the Invention
The present invention relates to a modular prosthesis for replacing a portion of a bone and the methods of assembly and use thereof.
2. The Relevant Technology
As the average age of society increases and the expected quality of medical treatment increases, the occurrence of surgical procedures to repair or replace worn arthritic joints correspondingly increases. Consequently, the surgical replacement of articulating joints is becoming more common. In the replacement of an articulating joint, one end of the prosthesis is placed within a bone on one side of a joint. Placing the prosthesis within the bone allows adequate mechanical stabilization between the bone and the implant. The opposite side of the prosthesis is configured to functionally replace the removed articulating end of the bone and provide a joint articulation surface.
The bone is prepared for the prosthesis by first resecting the bone and removing the damaged articulating end of the bone. This exposes the inside of the bone. Then, in the case of long bones, tools such as reamers, broaches and other bone tissue removal instruments are used to create a bone cavity that extends from the resection down into the intramedullary canal. Oftentimes bone cement is then added to the cavity, creating a bone cement mantle between the prosthesis and the bone. Sometimes the shape cavity is prepared to closely match external surface of the prosthesis, and no bone cement is used.
Once the bone cavity is prepared, the prosthesis is placed into the bone cavity and is supported by the internal bone tissue or bone cement mantle. Then, the prosthesis is positioned such that the articulating end of the implant articulates with the opposite side of the natural joint in the case of a hemiplasty, or articulates with a corresponding implant replacing the opposite side of the joint in the case of an arthroplasty.
A successful joint replacement procedure restores the biomechanical function of the joint while maintaining a secure interface with the bone, allowing the loads on the joint to be distributed optimally. A closely matching fit between the prosthesis and the bone tissue helps to stabilize the prosthesis and transfer the loads from the implant to the bone efficiently. Operating room centers need to keep in inventory an extraordinary number of single piece prostheses to provide single piece prostheses that optimally fit each size and shape of patient requiring a joint replacement surgery. With single piece prostheses, one compromise is to stock fewer prostheses shapes and sizes. However, this results in some patients receiving prostheses that are not ideally suited for their bone anatomy.
Modular components of joint reconstruction implants have been developed as an alternative to single piece joint reconstruction prostheses to help reduce inventory and optimize fit. The functional portions of single piece joint prostheses are sectioned into modular components. Each of these components is available in a variety of shapes and a range of sizes. Shapes and sizes of each component in the range that best fits a given patent's anatomy are supplied to the surgeon at the time of surgery. The surgeon selects the optimal combination of components to build the best fitting prosthesis. These modular components are then mated together and secured by locking the mechanical connections between them.
A successful modular implant system is one that provides the surgeon with a wide range of anatomical shapes and sizes, limits the inventory needed on hand, and provides reliable mating connections between the components. Successful application of the modular implants depends on careful selection, insertion, positioning and assembly of the components to best fit the existing bone and to restore the natural anatomy. To achieve this, it is important that the modular implant design allow for a functional and practical assembly process that results in strong mechanical bonds between the components.